Zinc is a critical element in the growth of humans. It is particularly important during stages of rapid growth as observed in newborn infants. Its presence is still more important if adequate stores are not present in the infant, such as in preterm infants. Although the importance of zinc in infants is appreciated, details of its metabolism and its requirements for growth are not well known. It is the purpose of this study to investigate the absorption, distribution, retention and excretion of zinc in stable term and preterm infants using the stable isotope of zinc 70ZN. This stable isotope will be administered orally and intravenously in three groups of infants based upon gestational age and with the use of neutron activation techniques and measurements of analysis of native zinc content in plasma, erythrocytes, urine, stool, muscle, subcutaneous tissue and other tissues of these infants will be made at various time periods. These kinetic data will be analyzed by deconvolution with a previously developed zinc model by which estimates of zinc mass in the various body zinc compartments will be obtained as will estimates of rate constants into and out of these compartments. With these techniques we will also be able to estimate total body zinc mass and the requirements for zinc nutrition which will hold the body system in equilibrium. It is important to obtain these data in preterm infants as early as possible in their life and it is difficult to perform studies during this period; the proposed methodology in this study is the only one available which allows these estimates to be made. Traditional balance studies yield data only about zinc absorption and excretion and will be most difficult to perform during these critical yet rapidly changing periods of infant life. The established expertise of the Georgetown group in the study of zinc metabolism in neonates and their development and use of mathematical modeling to deal with these types of data make their contribution unique. The established expertise of the University of Maryland group in the field of nuclear chemistry makes their contribution also unique. The association between these two groups of scientists offer a special opportunity to obtain data of extreme importance in this area of knowledge. The results to be obtained can specify the level and characteristics of any abnormality of zinc metabolism in these infants, can be utilized rapidly on a clinical level to maintain adequate zinc nutrition and hopefully can specify mechanisms where by clinical zinc deficiencies in neonates can be prevented.